Entangled State Quantum Cryptography: Eavesdropping on the Ekert Protocol
Devang Naik, Charles G. Peterson, Andrew G. White, Andrew J. Berglund, Paul G. Kwiat · Physical Review Letters · 2000
Using polarization-entangled photons from spontaneous parametric down-conversion, we have implemented Ekert's quantum cryptography protocol. The near-perfect correlations of the photons allow the sharing of a secret key between two parties. The presence of an eavesdropper is continually checked by measuring Bell's inequalities. We investigated several possible eavesdropper strategies, including pseudo-quantum-nondemolition measurements. In all cases, the eavesdropper's presence was readily apparent. We discuss a procedure to increase her detectability.